For something like this, it’s not a problem.
Thank you. 
A siphon can start even if the pipe goes above the water level, or there’s a bend in the pipe (otherwise you’d never be able to drain a tank from the top with one), so yes, 1 and 2 would both start siphoning in case of a power failure.
By the way, without knowing how fast the throughput is for your sump, it’s impossible to say if it’ll be sufficient filtration. The size of the sump isn’t really the important bit, it’s the contents and the water flow that are.
The green pipe would absolutely work. Drill a small hole just below the water line and it will break siphon when the water level gets low enough to allow air into the line. As long as you account for that drainage when you decide how much water you want to have in your sump you’ll be fine.
You really want two drains though, IMO. If you only have one it could clog, and if you are still pumping water into the display tank without a drain capable of matching or exceeding that flow rate you’ll flood your house.
Any other questions feel free to ask, I have a drilled freshwater tank with a sump and I learned a lot through trial and error putting it together.
Emtar, is your stuff fresh or salt water?
Fresh. I just have some cichlids.
Cool!
Tanganyika by any chance?
Need some Pulchers?